An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A transparent plate inserted in one of the arms of an interferometer, in particular the → Michelson interferometer, to compensate for a longer → optical path in the other arm. Its function is to ensure that the beams transverse the same total thickness of glass in both arms of the interferometer. This is not essential for producing → interference fringes in monochromatic light. The compensator plate is of the same glass and the same thickness as the → beam splitter plate.

→ compensator; → plate.

1) To look at with continued attention.
2) To think about intently and at length.

From L. contemplatus, from contemplari "to gaze attentively, observe," from → com- + templum "space marked out for observation of auguries."

Darnegaristan "contemplate, think deeply," from prefix dar- "→ in-, into," + negaristan "to look," → theory.

A large glass plate placed at the entrance of a Schmidt telescope to correct for spherical aberration over the large field of view.

→ correct; → plate.

A plate of optical material whose thickness is such that the phase difference between the extraordinary and ordinary rays after passing through the place is exactly one-half cycle. It can serve to rotate the plane of polarization of a light beam.

→ half; → wave; → plate.

A piece of glass with plane parallel surfaces used to admit light into an optical system and to exclude dirt and moisture.

→ plane; → parallel; → plate.

1) Optics: Any crystalline material whose length is much less than its measured diameter. → half-wave plate.
2) A flat piece of material on which a picture or text has been produced.
3) Any of the large movable segments into which the Earth's lithosphere is divided. → plate tectonics.

M.E., from O.Fr. plate "thin piece of metal," from M.L. plata "plate, piece of metal," perhaps via V.L. *plattus, from Gk. platys " flat, broad."

1) Tiqé, from tiq "blade," related to tiz "sharp," variants tig, tež, tej, tij; Mid.Pers. tigr, têz, têž "sharp," O.Pers. tigra- "pointed," tigra.xauda- "pointed helmet (epithet of Scythians)," Av. tiγra- "pointed," tiγray- "arrow," tiži.arštay- "with the pointed spear," cf. Skt. tikta- "sharp, pungent, bitter," tejas- "sharpness, edge, point or top of a flame;" PIE base *st(e)ig- "to stick; pointed." Cognates in other IE languages: Gk. stizein "to prick, puncture," stigma "mark made by a pointed instrument," L. in-stigare "to goad," O.H.G. stehhan, Ger. stechen "to stab, prick," Du. stecken, O.E. sticca "rod, twig, spoon," E. stick.
2); 3) loanword from Fr., as above.

The celestial coordinates of the center of the field of an astronomical photographic plate.

→ plate; → center.

The scale factor for converting linear measure on a photographic plate to angular measurement on the sky.

→ plate; → scale.

The theory supported by a wide range of evidence in which the Earth's crust is composed of several large, thin, relatively rigid plates that move relative to one another. The interaction of the plates at their boundaries causes seismic and tectonic activity along these boundaries. See also → continental drift.

→ plate; → tectonics.

1) An extensive area with a fairly level surface raised sharply above adjacent land.
2) A period, phase, or state of little or no growth or decline in something. → Spite plateau.

From Fr. plateau, from O.Fr. platel "flat piece of metal, wood, etc.," diminutive of plat "flat surface or thing," → plate.

Taxtâl, from taxt "flat;" Mid.Pers. taxtag "tablet, plank, (chess)board" + -âl, → -al.

1) A small platelike body.
2) One of a variety of forms taken on by → snowflakes.
3) A tiny cell occurring in the blood of vertebrates and involved in clotting of the blood. Formerly called thrombocyte.

→ plate; → -let.

A plate of doubly refracting material cut parallel to the optic axis of the crystal and of such a thickness that a phase difference of 90° is introduced between the ordinary and extraordinary rays for light of a particular wavelength. → half-wave plate.

→ quarter; → wave; → plate.

Same as → wave plate.

→ retardation; → plate.

An almost horizontal region in the → CMB angular power spectrum belonging to a → multipole index 10 ≤ l ≤ 100. This feature is due to the → Sachs-Wolfe effect.

→ Sachs-Wolfe effect; → plateau.

The observation that the abundance of → lithium (⁷Li) in metal-poor stars is constant regardless of the → effective temperature (> 5500 K) and the → metallicity ([Fe/H] < -2). The Spite plateau is currently interpreted as evidence that the Li observed in → halo population stars is → primordial. Since its discovery, the Spite plateau has been subject to numerous investigations, increasing the number of stars with Li measurements and extending the sample to include ever lower metallicities. Important issues are the existence or not of a significant scatter along the plateau, and the existence or not of atomic diffusion and mixing with deeper stellar zones where Li can be burnt, producing an offset with respect to the → Big Bang → nucleosynthesis abundance. Several recent studies have shown that the Spite plateau exhibits very little, if any, dispersion. There is, however, a discrepancy between recent results and that derived from Big Bang nucleosynthesis, based on the cosmological parameters constrained by the → WMAP measurements.

Named after François and Monique Spite, French astronomers, Paris Observatory, who first discovered this relation (1982, A&A 115, 357); → plateau.

An optical element that retards the phase of one plane of vibration of light relative to the plane at right angles. The two beams then recombine to form a single beam with new polarization characteristics. A typical wave plate is a birefringent crystal with a carefully chosen orientation and thickness. Also known as → retardation plate. A → half-wave plate creates a half-wave retardation. See also → quarter-wave plate.

→ wave; → plate.